Introduction – humans, nature and human nature - Ecological Applications: Toward a Sustainable World - page 8

Fig. 1.5 Extinctions in
Singapore since the
early 1800s - green
(light) and blue (dark)
bars represent recorded
and inferred extinc-
tions, respectively.
(After Sodhi
et al., 2004.) (This
fi gure also reproduced
as color plate 1.5.)

Extinctions in Singapore

Mammals

Singapore in 1819

Birds

Reptiles

Amphibians

Fish

Singapore in 1990

Butterfiles

Phasmids

Primary rainforest

Decapod crustaceans

Freshwater swamp forest
Mangrove
Secondary forest
Urban and cultivated area

Plants

100 90 80 70 60 50 40 30 20 10 0

Percentage of species extinct

produce new biomass (primary productivity), the rate at which dead organic matter
decomposes, and the extent to which nutrients are recycled from dead organic
matter back to living organisms. These processes are so fundamental that a substan-
tial change in any one will ramify throughout the food web.
Note, fi rst, that ecosystem properties are not invariably sensitive to a reduction
in biodiversity. It may be, for example, that different species carry out similar func-
tional roles and can 'cover for each other' should some be lost. In addition, some
species only contribute a little to productivity (or decomposition or nutrient cycling)
so their loss would barely register. Other species, however, contribute more
than their fair share - the extinction of one of these would be strongly felt (Hooper
et al., 2005).
Of most signifi cance is the question of whether species are 'complementary' in
the way they operate. If they are, then higher biodiversity will generally equate to
higher productivity (or decomposition rate, or nutrient recycling). Take, for example,
a set of grassland experiments carried out in Europe (Figure 1.6a). Plant biomass at
the end of the growing season was higher when each of three different functional
groups was represented (grasses, forbs (nongrass herbs) and nitrogen-fi xing
legumes). Similarly, the rate of breakdown of tree leaves that fall into streams is
higher when the richness of detritivorous insect species is higher (because they
'shred' and feed on the leaves in different ways) (Figure 1.6b). In these cases,
then, loss of species is likely to have a detectable impact on the way an ecosystem
functions. Managers need to beware loss of biodiversity, both for the sake of the
species concerned but also because of consequent changes to ecosystem
processes.